1. Field of the Invention
The present invention generally relates to data processing and more particularly to accessing data independent of the particular manner in which the data is physically represented.
2. Description of the Related Art
Databases are computerized information storage and retrieval systems. A relational database management system is a computer database management system (DBMS) that uses relational techniques for storing and retrieving data. The most prevalent type of database is the relational database, a tabular database in which data is defined so that it can be reorganized and accessed in a number of different ways. A distributed database is one that can be dispersed or replicated among different points in a network. An object-oriented programming database is one that is congruent with the data defined in object classes and subclasses.
Regardless of the particular architecture, in a DBMS, a requesting entity (e.g., an application or the operating system) demands access to a specified database by issuing a database access request. Such requests may include, for instance, simple catalog lookup requests or transactions and combinations of transactions that operate to read, change and add specified records in the database. These requests are made using high-level query languages such as the Structured Query Language (SQL). Illustratively, SQL is used to make interactive queries for getting information from and updating a database such as International Business Machines' (IBM) DB2, Microsoft's SQL Server, and database products from Oracle, Sybase, and Computer Associates. The term “query” denominates a set of commands for retrieving data from a stored database. Queries take the form of a command language that lets programmers and programs select, insert, update, find out the location of data, and so forth.
One of the issues faced by data mining and database query applications, in general, is their close relationship with a given database schema (e.g., a relational database schema). This relationship makes it difficult to support an application as changes are made to the corresponding underlying database schema. Further, the migration of the application to alternative underlying data representations is inhibited. In today's environment, the foregoing disadvantages are largely due to the reliance applications have on SQL, which presumes that a relational model is used to represent information being queried. Furthermore, a given SQL query is dependent upon a particular relational schema since specific database tables, columns and relationships are referenced within the SQL query representation. As a result of these limitations, a number of difficulties arise.
One difficulty is that changes in the underlying relational data model require changes to the SQL foundation that the corresponding application is built upon. Therefore, an application designer must either forgo changing the underlying data model to avoid application maintenance or must change the application to reflect changes in the underlying relational model. Another difficulty is that extending an application to work with multiple relational data models requires separate versions of the application to reflect the unique SQL requirements driven by each unique relational schema. Yet another difficulty is evolution of the application to work with alternate data representations because SQL is designed for use with relational systems. Extending the application to support alternative data representations, such as XML, requires rewriting the application's data management layer to use non-SQL data access methods.
A typical approach used to address the foregoing problems is software encapsulation. Software encapsulation involves using a software interface or component to encapsulate access methods to a particular underlying data representation. An example is found in the Enterprise JavaBean (EJB) specification that is a component of the Java 2 Enterprise Edition (J2EE) suite of technologies. In accordance with the EJB specification, entity beans serve to encapsulate a given set of data, exposing a set of Application Program Interfaces (APIs) that can be used to access this information. This is a highly specialized approach requiring the software to be written (in the form of new entity EJBs) whenever a new set of data is to be accessed or when a new pattern of data access is desired. The EJB model also requires a code update, application built and deployment cycle to react to reorganization of the underlying physical data model or to support alternative data representations. EJB programming also requires specialized skills, since more advanced Java programming techniques are involved. Accordingly, the EJB approach and other similar approaches are rather inflexible and costly to maintain for general-purpose query applications accessing an evolving physical data model.
Another shortcoming of the prior art, is the manner in which information can be presented to the user. A number of software solutions support the use of user-defined queries, in which the user is provided with a “query-building” tool to construct a query that meets the user's specific data selection requirements. In an SQL-based system, the user is given a list of underlying database tables and columns to choose from when building the query. The user must decide which tables and columns to access based on the naming convention used by the database administrator, which may be cryptic, at best.
Further, while the number of tables and columns presented to the user may be vast, only a limited subset may actually be of interest. Therefore, nonessential content is revealed to the end user, which may make it difficult to build a desired query, as the nonessential content must be filtered out by the user. In other words, in a conventional data model, a single database schema encompasses all the data for an entity, although individual groups within the entity (teams, workgroups, departments, etc.) are typically only interested in a limited portion of the data. For example, in a medical research facility, a hemotology research group may only be interested in a limited number (e.g., 20–40) of medical tests, while an entity-wide data model may encompass thousands of tests. Accordingly, when building a query, members of the hemotology research group may spend a lot of effort just to filter through the large number of tests for which they have no interest.
Therefore, there is a need for an improved and more flexible method for presenting, to a user, a limited subset of all possible fields to choose from when building a query. Preferably, the limited subset will only include fields of interest to the user.